The present disclosure relates to novel visually transparent, projectile-proof panels suitable for window systems of every type: armored vehicles, banks, schools, jewelry stores, embassies, hospitals, courtrooms, correction facilities, home storm windows, particularly hurricane windows, and the like. The disclosed novel panels and window systems are also useful for eye protection for helmets, goggles, military headwear, police protection and in application wherein the user needs to have protection from bullets, fragmentation (frag), and explosive debris including projectiles of extremely high speed. Further, the disclosed projectile-proof panels and window systems allow the user to continue to see through the projectile-proof panels and windows even after the bullet, frag or projectile has impacted the inventive window.
Bullet-proof and projectile-proof glass (also known as ballistic glass, transparent armor, or bullet-resistant glass) is a type of strong but optically transparent material that is particularly resistant to being penetrated when struck. It is made from laminated glass, in which two or more sheets of glass are laminated together with two or more plastic sheets, oftentimes with high levels of heat treatment to cause significantly high adhesion of the glass sheets to the plastic laminating materials. These sheets are typically bonded together using adhesive interlayers such as polyvinyl butyral, polyurethane, ethylene vinyl acetate, epoxy resin systems or combinations thereof. The index of refraction for all sheets used in the bulletproof layers must be almost the same to keep the glass transparent and allow a clear, undistorted view through the glass.
It is known that higher levels of bullet/projectile resistance may be achieved by increasing the thickness of the laminates, either thicker glass or thicker plastic, or by increasing the number of glass sheets or plastic sheets, to the detriment of light transmission through the glass. Bullet-proof glass typically varies in thickness from ¾ to 3½ inches (19 to 89 mm). At these thicknesses, weight becomes a critical and overruling parameter in applications such as in goggles, helmet eye protection, even car windows or bank windows, and the like.
Increasing the number layers of glass, plastic and/or adhesive are also known to provide for higher protection from bullet and projectiles. However, the increases in the number of layers results in higher weight, higher cost and decreased visibility.
It is known, for example in U.S. Pat. No. 7,584,689 to Jones etal, that increasing the thickness of composites, either glass, ceramic, plastic or combinations thereof will improve the penetration resistance of a projectile. For example, a 21.2 mm thick composite weighing 1.22 kg (2.68 pound) will prevent penetration by a 7.62×51 M-80 ball travelling at 2739 fps (feet per second), but the same ball at 2834 fps will penetrate. Increasing the thickness of the composition to 29.4 mm and weight to 1.63 kg (3.59 pounds) will prevent penetration. While useful in many applications, the composites are thick, heavy and expensive. Which prevents them from being used in other applications, such as, for example, goggles, protective helmets, windows of space vehicles, which protect the eyes and other desired protections.
It has been ingrained in the safety glass and bullet-proof technology that any layers of the safety glass or bullet-proof construction must be laminated together to provide a continuous composite structure. The rule being that when a projectile hits the safety glass or bullet-proof structure, spalling occurs, and small splinters of the glass, ceramic or other materials will fly around and possibly cause injury. Bonding of the layers helps to prevent this. However, when the glass, ceramic or other material spalls and shatters, there are always a plethora of cracks, lines, spider-webbing and the like. These make the structures opaque in that it is impossible to see through the area which has been struck by a projectile. In cases where the safety glass or bullet-proof structure is in large format there are other areas which provide sight. However, projectile-proof goggles or helmets or other smaller format devices fitted with protective eye gear are not of large format and do not have the luxury of other areas to be used for sight, and thus spalling, cracking, spider-webbing and other sight-preventing defects from a projectile strike make it virtually impossible to see, such that, the wearer either needs to remove the protective devices in order to flee the area or must dangerously stumble to remove him/her self from harm. The lamination construction of these bullet-proof and safety glass maintains all the glass shards and other defects intact. Additionally, in the case of military or police uses, with the now opaque goggles or helmet eye gear, the wearer cannot make the decision to continue fighting when such a decision is necessary for survival.
When a weight reduction is needed 3mm of polycarbonate (a thermoplastic) is laminated onto what would be considered the inside, or safe side of the panel. This polycarbonate stops the spall and by doing so maintains the cracks, spider-webbing and other sight-preventing defects in the glass. The aim is to make a material with the appearance and clarity of standard glass but with effective protection from small arms
The plastic in laminate designs also provides resistance to impact from physical assault from blunt and sharp objects. The plastic provides little in the way of bullet-resistance. The glass, which is much harder than plastic, flattens the bullet, and the plastic deforms, with the aim of absorbing the rest of the energy and preventing penetration. The ability of the polycarbonate layer to stop projectiles with varying energy is directly proportional to its thickness, and bulletproof glass of this design may be up to 3.5 inches thick. Again, this thickness limits its usefulness is many important and desirable applications.
All safety glass is designed so that all the layers, fragments and spalling, will remain intact after bullet, frag or projectile impact. This is suggested as a desirable feature so that glass fragments do not eject from the surface when impacted and possibly cause scratches or other shard related issues. By adhering all the layers together, they jointly absorb all the energy of the bullet, frag or projectile. Because the layers absorb all the energy of the bullet, the material weakens during impact, so that the ability to prevent bullet with high impact speed/energy from penetrating the bulletproof glass is limited. In order to improve the impact resistance of high speed/energy bullets, the layers must be thicker, which, by doing so, increases the weight and thus limits the applications into which the bulletproof glass may be used.
It is also well known that when the currently available bulletproof glasses are impacted by a bullet, frag or projectile the glass will spall and generate an enormous amount of cracking, spidering and shattering, so that the glass becomes totally opaque. When this happens in goggles or the sight port of a helmet, the person using the helmet or goggles can no longer see, and thus needs to remove the helmet or goggles in order to retreat, leave or perform any other activity after the bullet has impacted the bulletproof glass. As can be seen, in many situations removing the protection can be extremely dangerous, even fatal, such as in combat situation where removing a helmet puts the user in severe danger.
Some recent systems use a “standoff” construction which includes layering two or more bulletproof glass laminates together with a space between them in order to absorb more of the energy from the bullets. Since typical bullet proof glass is 20 mm thick, and common laminate safety glass is about 5 mm thick, an overall width for the system was chosen as about 75 mm, to avoid an impractically thick overall window system, indicating a desired standoff gap in the 50-65 mm range. These systems are very thick and high in weight resulting in a significant limit to their usefulness. For example, U.S. Pat. No. 7,174,692 to Vickers etal disclose the use of an air gap between two glass/plastic multilayer laminated panels which include dampening structures between the panes to absorb energy. The system also uses the release valves between the panels to allow air from the air gap to release when pressure from a projectile strikes the panel. No dimension of the gap is disclosed. Again, multilayer laminated panels are central to the disclosure. Also, this system is heavy, expensive and unsuitable for many applications where there is need for a light weight, inexpensive, and uncomplicated projectile-proof panel is required.
Thus, there is an unmet need for improved projectile-proof glass systems which can withstand the impact of high speed/energy projectiles while at the same time reduces the weight of the glass and provide visibility after impact and thus provide broader applications. Also, one unmet need is to provide projectile-proof panels and systems through which maintains a high level of transparency after being struck by a projectile allowing a person to maneuver without removing the panel or system.